Effects of Perpendicular Blade-Vortex Interaction, Part 1: Turbulence Structure and Development

Abstract

Three-component velocity and turbulence measurements were performed to document the turbulent flowfield produced downstream of an airfoil encountering an intense streamwise vortex. This configuration serves as a model for perpendicular blade-vortex interactions, which commonly occur in helicopter rotor flows. In the first part of a two-part paper, detailed measurements and analysis of a single flow-that produced by a vortex passing 1/8th chord from the blade-are presented with the objective of revealing the physics and providing a computational test case. It is shown that the vortex passes the blade without immediate change in the form and structure of its core. However, outside the core the flow is modified by the blade wake, which contains negative streamwise vorticity shed as a result of the angle-of-attack distribution induced on the blade by the vortex. This negative vorticity and the turbulent motions of the blade wake then appear to trigger the turbulent decay of the vortex core, resulting in an increase in its size, reduction in its strength, and loss of circulation as its vorticity is partially canceled